Priority based arbitration for TDMA schedule enforcement in a multi-channel system

ABSTRACT

A multi-channel TDMA network having priority based is provided. A network includes a plurality of channels, and a plurality of nodes adapted to transmit and received data. Through each channel, every node is coupled to communicate data with every other node. Within each channel, each node is assigned a unique priority rank. Only the node with the highest priority rank is permitted to transmit data during a time slot. For each channel of the multi-channel network, the plurality of nodes are ranked in a different priority direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the benefit of the filing dateof U.S. Provisional Application No. 60/523,785 entitled “PRIORITY BASEDARBITRATION FOR TDMA SCHEDULE ENFORCEMENT IN A DUAL LINK SYSTEM” filedon Nov. 19, 2003, and U.S. Provisional Application No. 60/560,323entitled “MESSAGE AUTHENTICATION IN A COMMUNICATION NETWORK” filed onApr. 6, 2004, and U.S. Provisional Application No. 60/523,782 entitled“HUB WITH INDEPENDENT TIME SYNCHRONIZATION” filed on Nov. 19, 2003, andU.S. Provisional Application No. 60/523,783 entitled “PARASITIC TIMESYNCHRONIZATION FOR A CENTRALIZED TDMA BASED COMMUNICATIONS GUARDIAN”filed on Nov. 19, 2003, all of which are incorporated herein byreference.

This application is also related to the following co-pendingapplications filed on even date herewith, all of which are herebyincorporated herein by reference:

-   -   U.S. patent application Ser. No. ______ (attorney docket number        H0005281-1633 entitled “PARASITIC TIME SYNCHRONIZATION FOR A        CENTRALIZED COMMUNICATIONS GUARDIAN”) and which is also referred        to here as the '5281 application;    -   U.S. patent application Ser. No. ______ (attorney docket number        H0007587-1633 entitled “PORT DRIVEN AUTHENTICATION IN A        NETWORK”) and which is also referred to here as the '7587        application; and    -   U.S. patent application Ser. No. ______ (attorney docket number        H0005031-1633 entitled “ASYNCHRONOUS HUB”) and which is also        referred to here as the '5031 application.

TECHNICAL FIELD

The following description relates to the field of electronics and inparticular, to priority based arbitration for TDMA based communicationprotocols.

BACKGROUND

Distributed, fault-tolerant communication systems are used, for example,in applications where a failure could possibly result in injury or deathto one or more persons. Such applications are referred to here as“safety-critical applications.” One example of a safety-criticalapplication is in a system that is used to monitor and manage sensorsand actuators included in the fields of automotive, aerospaceelectronics, industrial control, and the like.

Architectures considered for safety-critical applications are commonlytime-triggered architectures where nodes use the synchronized time tocoordinate access to common resources, such as the communication bus.One architecture that is commonly considered for use in suchsafety-critical applications is the Time-Triggered Architecture (TTA).In a TTA system, multiple nodes communicate with one another over tworeplicated high-speed communication channels using, for example, atime-triggered protocol such as the Time-Triggered Protocol/C (TTP/C).

Fault-tolerant protocols (e.g. TTP/C) that use time-division multipleaccess (TDMA) as the medium access strategy where each node is permittedto periodically utilize the full transmission capacity of the bus forsome fixed amount of time called a TDMA slot. As long as each node usesonly its statically assigned TDMA slot, collision free access the buscan be assured.

Typically, transmissions of messages by nodes in a TTP network arecontrolled by a schedule table which determines which node haspermission to transmit for each TDMA slot, and also defines the startingtime and duration of the TDMA slot. This starting time and durationdefines a node's permitted transmission window. A node's transmitterstarts to send its message after the start of its window, and shouldfinish before it is over. Nodes without permission to transmit listenfor transmissions when a TDMA slot begins until the duration haselapsed. The timing of when a node transmits and receives is controlledby a node's local clock that is synchronized to other nodes in thesystem, by a distributed clock synchronization algorithm. In practice,the perfect synchronization of all of the nodes' clocks is not possibleso that the clocks for each node are slightly skewed from each other.Because of this, it is possible that a node's transmitter may begin totransmit a message before one or more of the receiving nodes are readyto listen. Similarly, it is possible for a node to continue transmissionafter the other nodes have stopped listening. Additionally, a degradednode may attempt to transmit well outside of its assigned window.

A centralized guardian has been conceived to limit the propagation ofsuch failures. These Guardians (or central guardians) ensure that adegraded node transmitter cannot broadcast to the network outside itsallotted window. At the beginning of a TDMA slot, after a predefineddelay, the guardian opens a window which allows a node to transmitmessages to the network. If the node is operating correctly, it willbegin transmission shortly after the guardian's window opens andcomplete transmission before the window closes. Ideally, receiving nodes(i.e. listening nodes) begin listening at the beginning of the TDMA slotuntil the guardian's window closes. The guardian blocks transmissionsfrom a node that does not occur within the transmission window.

One problem with the current state of the art for guardians is thatrealizations of guardian functions have been required to duplicate theprotocol logic engine implemented at the nodes in order to haveindependent knowledge of the communication schedule and timingparameters, such as slot order, transmission start time, etc.Implementation of the protocol logic engine within the guardian has ledto highly complex guardian designs. With the centralization of theguardian's roll in regards to network data flow, guardians themselveshave become critical architecture components. The complexity of aguardian design is a significant issue with respect to the viability ofa design in safety critical applications. For example, in some casesgate level failure analysis is required before a guardian design may beused for safety critical applications. In these cases, the complexity ofperforming a failure analysis for such a guardian has significantfinancial impact in terms of product development costs. In someapplications guardian circuitry may be required to perform self-tests toascertain its own health. The complexity of these self-tests is alsodirectly related to the complexity of the guardian.

Another problem is that for some protocols, current guardian designsbased on internally implementing protocol logic engines requires thatguardian within a network be coupled together. Embodiments of thepresent invention eliminate this requirement.

It has further introduced the possibility of failure in the form ofinconsistency between the guardian and the nodes it is protecting.Requiring the guardian to maintain knowledge of current or past states,in the form of transmission orders, leaves the implementation vulnerableto state upsets, which can be induced by environmental factors such ashigh energy neutrons.

For the reasons stated above and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the specification, there is a need in the art for asimplified guardian design.

SUMMARY

Embodiments of the present invention enable a simple priority basedarbitration mechanism to be realized in a central guardian of a TDMAbased protocol communication network. In place of realizing a fullprotocol engine with schedule knowledge within a guardian, embodimentsof the present invention enable a central guardian to arbitrate betweenthe system's member nodes attempting to communicate on the networksimultaneously.

In one embodiment, a multi-channel network having priority basedarbitration is provided. The network comprises a plurality of nodes,wherein each node is adapted to transmit and receive data and two ormore hubs, each hub having communication links with the plurality ofnodes. Each node is adapted to communicate with every other node throughthe one or more hubs and the communication links between any one hub andthe plurality of nodes defines a first channel. The network furthercomprises two or more guardians, wherein each guardian is associatedwith one hub and each node is adapted to transmit through the channelduring a time slot. For each channel of the multi-channel network, eachnode is assigned a unique priority rank such that no two nodes on onechannel have the same assigned priority rank. For each channel, thepriority ranks for each of the plurality of nodes are in differentdirections. A first guardian of the two or more guardians for anassociated hub determines which node is permitted to transmit during atime slot by permitting only a winning node with the highest assignedpriority rank to transmit through the channel.

In another embodiment, a network is provided. The network comprises aplurality of sub-networks and a plurality of nodes adapted to transmitand received data. Through each sub-network, every node is coupled tocommunicate data with every other node. For each sub-network, each nodeis assigned a unique priority rank. A winning node of the plurality ofnodes is identified as having the highest priority rank for at least onesub-network and is permitted to transmit data during a time slot. Foreach channel the nodes are ranked in a different priority direction.

In yet another embodiment, a method for priority based arbitration for acentral guardian of one channel of a TDMA multi-channel network isprovided. The method comprises assigning a unique priority rank to eachnode coupled to the one channel, observing the receipt of a firstpreamble signal indicating the intention of a first node of theplurality of nodes to transmit during the time slot, and observing thereceipt of a second preamble signal indicating the intention of a secondnode of the plurality of nodes to transmit during the time slot within apredefined time interval of observing the receipt of the first preamblesignal. When the first node has a higher priority rank than the secondnode, the method further comprises allowing only the first node totransmit through the one channel during the time slot. When the secondnode has a higher priority rank than the first node, the method furthercomprises allowing only the second node to transmit through the onechannel during the time slot. For each channel of the multi-channelnetwork, the unique priority rank direction is different.

In yet another embodiment, a multi-channel network is provided. Thenetwork includes a means for priority based arbitration for acentralized guardian with a plurality of nodes. The network furtherincludes means for assigning a unique priority rank to each node of aplurality of nodes coupled to a first channel of the multi-channelnetwork, a means for observing the receipt of a first preamble signalindicating the intention of a first node of the plurality of nodes totransmit during a time slot and a means for observing the receipt of asecond preamble signal indicating the intention of a second node of theplurality of nodes to transmit during the time slot within a predefinedtime interval of observing the receipt of the first preamble signal. Thenetwork further comprises a means for allowing only the first node totransmit during the time slot, when the first node has a higher priorityrank than the second node; and a means for allowing only the second nodeto transmit during the time slot when the second node has a higherpriority rank than the first node. For each channel of the multi-channelnetwork, the unique priority rank direction is different.

In yet another embodiment a computer-readable medium havingcomputer-executable instructions for performing a method of prioritybased arbitration for a central guardian of one channel of a TDMAmulti-channel network is provided. The method comprises assigning aunique priority rank to each node of a plurality of nodes coupled to theone channel, observing the receipt of a first preamble signal indicatingthe intention of a first node of the plurality of nodes to transmitduring a time slot, and observing the receipt of a second preamblesignal indicating the intention of a second node of the plurality ofnodes to transmit during the time slot within a predefined time intervalof observing the receipt of the first preamble signal. When the firstnode has a higher priority rank than the second node, the method furthercomprises allowing only the first node to transmit through the onechannel during the time slot; and when the second node has a higherpriority rank than the first node, the method further comprises allowingonly the second node to transmit through the one channel during the timeslot. For each channel of the multi-channel network, the unique priorityrank direction is different.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more easily understood and furtheradvantages and uses thereof more readily apparent, when considered inview of the description of the preferred embodiments and the followingfigures in which:

FIG. 1 is a block diagram of a dual-channel network of one embodiment ofthe present invention;

FIG. 2 is a block diagram of a multi-channel network of one embodimentof the present invention;

FIG. 3 is an arbitration timing diagram of one embodiment of the presentinvention;

FIG. 4 is a block diagram of another multi-channel network of oneembodiment of the present invention;

FIGS. 5 a and 5 b are arbitration timing diagrams of other embodimentsof the present invention;

FIG. 6 is a block diagram of another multi-channel network of oneembodiment of the present invention; and

FIG. 7 is a flow chart of a method of an embodiment of the presentinvention.

In accordance with common practice, the various described features arenot drawn to scale but are drawn to emphasize features relevant to thepresent invention. Reference characters denote like elements throughoutFigures and text.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of illustration specific illustrative embodiments in which theinvention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that logical, mechanical and electrical changes may be madewithout departing from the spirit and scope of the present invention.The following detailed description is, therefore, not to be taken in alimiting sense.

Embodiments of the present invention enable a simple priority basedarbitration mechanism to be realized in a central guardian of a TDMAbased protocol communication network. In place of a full protocol enginewithin the guardian, embodiments of the present invention enable acentral guardian to arbitrate access to the communications channelbetween member nodes, each of which already implement full protocolengines themselves. Embodiments of the present invention do not requirethe central guardian to know the underlying protocol in regards to whichnode is permitted to transmit during which TDMA slot. However, forsingle failure tolerant network designs, the availability of networkcommunications achieved using the present invention is equivalent tothat of guardians executing full protocol enforcement. Requiring nospecific knowledge of protocol behavior, the present invention enablesvery simple synchronization logic to be realized.

This invention differs from previous systems, as it prevents datacollisions caused by two nodes transmitting on a channel simultaneously,without duplicating the protocol logic engine of the nodes within theguardian. This has advantages over the current practice including muchless complex implementations and simplified guardian failure analysisfor safety critical domains, and removes guardian dependency on protocolstate logic and signals.

The invention presented exploits the fact that in many networks channelsare often duplicated to ensure the continued availability of datacommunications and fault tolerance. Utilizing the nature ofmulti-channel networks, it is possible to soften the requirements forguardian enforcement decisions relative to current state of the artguardians. Instead of guaranteeing that only the correct node will beallowed transmit data on a channel during a TDMA slot, embodiments ofthe present invention guarantee that 1) only one node will be allowed totransmit data over a given channel, and 2) the correct node (i.e. thenode that according to protocol is permitted to transmit during a TDMAslot) has exclusive access to at least one channel in order to transmitits data. Because the purpose of duplicated channels in theseapplications is for availability assurance only, such a philosophy isconsistent with the underlying assumptions of such protocols. Using sucha design rationale, the implementation of a centralized guardian can berealized based on a simple priority based arbitration circuit.

FIG. 1 is a block diagram of one embodiment of multi-channel network,shown generally at 100, according to the teachings of the presentinvention. Although FIG. 1 illustrates a dual channel network forsimplicity, it would be readily understood by one skilled in the artupon reading this specification that embodiments of the presentinvention also readily apply to networks with greater than two channels.Network 100 includes a plurality of nodes 102-1 to 102-N. In thisembodiment, network 100 includes a plurality of nodes 102-1 to 102-Neach coupled to hubs 104-1 and 104-2. In one embodiment, data istransmitted in frames from one node 102-1 to 102-N to another in network100 through hubs 104-1 and 104-2. In one embodiment, each sub-networkcomprising communication links between an individual hub and theplurality of nodes 102-1 to 102-N defines a single network channel. Inone embodiment, network 100 operates as a dual channel system where hub104-1 operates to distribute data communications on the “0” Channelbetween nodes 102-1 to 102-N and hub 104-2 operates to distribute datacommunications on the “1” Channel between nodes 102-1 to 102-N. In oneembodiment, one or more electronic devices 106-1 to 106-P are connectedto nodes 102-1 to 102-N. In one embodiment, electronic devices 106-1 to106-P include sensors, processors, actuators, controllers, input devicesand the like that communicate data frames over network 100.

Network 100 operates on a time division multiple access (TDMA) basedcommunication protocol where each node 102-1 to 102-N is assigned atransmission TDMA slot order. In such a network each node independentlyimplements the protocol and has full knowledge of the current protocolstate (i.e. each node independently knows the state of which TDMA slotis the current TDMA slot, the time the current TDMA slot's transmissionwindow will open, the time the current TDMA slot's transmission windowwill close, whether the node has permission to transmit during thecurrent TDMA slot's transmission window, as well as which TDMA slot isthe next TDMA slot and future TDMA slots.)

Hubs 104-1 and 104-2 each include a central guardian 103-1 and 103-2that functions to regulate the propagation of data communications fromnodes 102-1 to 102-N through each associated channel. In order to reducethe complexity of the guardian 103-1 and 103-2 function the presentinvention provides a simple priority based arbitration protocol.

Priority based arbitration for network 100 is achieved as follows: Inone embodiment, in operation, each node 102-1 to 102-N is designated afirst priority scheme on Channel 0 and a second priority scheme onChannel 1. For example, in one embodiment nodes 102-1 to 102-N have anincreasing associated priority of 1 through N on Channel 0. On Channel1, the priority is reversed so that nodes 102-1 to 102-N have adecreasing associated priority of N through 1. For each associatedchannel, guardians 103-1 and 103-2 only allow propagation of datathrough hub 104-1 and 104-2 transmitted by the highest priority nodeattempting to transmit during a time slot. Ideally, each node 102-1 to102-N has full accurate knowledge of whether it is permitted to transmitduring the current TDMA slot and only one node 102-1 to 102-N willattempt to transmit data over the channel during any single TDMA slot.Under these conditions, the guardian 103-1 and 103-2 plays a passiverole because no arbitration over channel transmission rights isrequired. However, under a single failure scenario, a degraded node ofnodes 102-1 to 102-N may attempt unauthorized transmissions during aTDMA slot assigned to another node 102-1 to 102-N. Under a priorityscheme of one embodiment of the present invention, if node 102-1 (forexample) attempts to transmit during 102-3's time slot, node 102-1 (witha priority of 1 on Channel 0) has priority over node 102-3 (which has apriority of 3 on Channel 0). Accordingly guardian 103-1 selects node102-1 as the “winning” node for this arbitration contest. Guardian 103-1denies node 102-3 access to transmit data over Channel 0 (even thoughnode 102-3 is authorized by protocol to transmit) because it alwayslooses priority arbitration battles with node 102-1 on this channel.However on Channel 1, node 102-3 always wins priority arbitrationbattles with node 102-1. Therefore, guardian 103-2 denies node 102-1access to transmit data over Channel 1 and allows access to node 102-3.As a result, node 102-3 will always be able to transmit data across atleast one channel during its assigned TDMA slot.

Under a single fault assumption with a network of at least two channelshaving different priority directions, embodiments of the presentinvention guarantee that a good transmission will get through on atleast one channel (i.e. a node properly transmitting during its assignedTDMA slot will be selected as a winning node on at least one channel.)In one embodiment, each TDMA slot is arbitrated without any history,using only the information sensed during a particular arbitrationperiod. In other embodiments, a guardian for a channel may incorporatehistorical information into the arbitration decision to try to determinewhich of multiple competing nodes is the correct node to allow totransmit over the channel (e.g. use history to eliminate certain nodesas contenders based on history of which nodes have recentlytransmitted.)

FIG. 2 is a block diagram of one embodiment of a multiple hub basednetwork, shown generally at 200, according to the teachings of thepresent invention. In this embodiment, network 200 includes a pluralityof nodes 202-1 to 202-N each coupled to a plurality of hubs 204-1 to204-H. In one embodiment, each sub-network comprising communicationlinks between an individual hub and the plurality of nodes 202-1 to202-N defines a single network channel. Priority based arbitration innetwork 200 operates on the same basis as the dual hub network 100described in the embodiments of FIG. 1.

Data is transmitted in frames from one node 202-1 to 202-N to another innetwork 200 through hubs 204-1 to 204-H. As described in for network 100of FIG. 1, in one embodiment, network 200 operates on a time divisionmultiple access (TDMA) based communication protocol where each node202-1 to 202-N has been assigned a transmission slot order (i.e. a TDMAslot) within the channel. In one embodiment, the network is a TTPnetwork and the TDMA slot is an SRU slot. Hubs 204-1 to 204-H eachincludes a central guardian 203-1 to 203-H that implements prioritybased arbitration of the present invention wherein guardian 203-1 to203-H have different priority direction for the nodes 202-1 to 202-N. Inone embodiment, under a single fault assumption, embodiments of thepresent invention guarantee that a good node transmission will getthrough on at least one channel of network 200, as long as at least onechannel has a guardian utilizing a different priority direction than theother channels. In another embodiment, the guardians 203-1 to 203-H eachemploy different priority schemes for the nodes 202-1 to 202-N. In oneembodiment, guardians 203-1 to 203-H are adapted with a memory thatholds the priority schemes in a table. In one embodiment, the memory ofguardians 203-1 to 203-H can be reprogrammed with different priorityschemes. In another embodiment, the priority of nodes 201-1 to 201-N isdetermined by which port on hubs 201-1 to 201-H each node is wired to.

FIG. 3 is an illustration of one embodiment of a priority basedarbitration timing diagram for a network such as network 200 describedwith respect to FIG. 2. FIG. 3 includes one or more preamble signals 320received from the nodes 202-1 to 202-N by a guardian 203 of one channelof network 200. A preamble signal received from a node indicates thatthe node sending the preamble signal intends to transmit data during thecurrent TDMA slot 355. In one embodiment, nodes 202-1 to 202-N sendpreamble signals 320 to guardian 203 on the same communications link(such as communications link 210) utilized to transmit and receive datacommunications. In one embodiment, nodes 202-1 to 202-N send preamblesignals to guardian 320 separate communications links (not shown) thanthose utilized to transmit and receive data communications.

At the start of the current TDMA slot 350, guardian 203 opens anarbitration window 330 of time π in duration. The bounded time intervalπ represents the maximum skew in the timing synchronization of nodes202-1 to 202-N that properly operating nodes 202-1 to 202-N are expectedto have. In some embodiments, arbitration window 330 has a duration timeof π plus a signal propagation delay constant. Guardian 203 waits for afirst preamble signal 325. If only one preamble signal is receivedduring an arbitration window 330, then no arbitration between nodes isrequired and guardian 203 will close arbitration window 330 and open atransmission window 340 for the node which sent the one preamble signal.This will allow that node to transmit data to other nodes on thechannel. In one embodiment, transmission windows 340 opens after apredefined time delay after arbitration windows 330 closes. Since eachnode 202-1 to 202-N knows that it is assigned (by protocol) a TDMA slotin which it is exclusively permitted to transmit, in a properlyoperating network, only a single preamble signal 325 is received byguardian 203 during arbitration window 330. Under a single faultassumption however, a faulty node may attempt to transmit during anothernode's TDMA slot. In that case, guardian 203 will receive two preamblesignals (325 and 326) from two different nodes during arbitration window330. Guardian 203 chooses which of the two nodes it will allow totransmit across the channel during TDMA slot 350. In one embodiment,guardian 203 arbitrates between the two nodes and allows only the nodewith the highest priority assignment to transmit across the channel. Tomake this arbitration decision, guardian 203 does not require knowledgeof which node should be allowed to transmit per the underlying protocol.Upon the start of the next TDMA slot, guardian 203 will opentransmission window 340 for the node with the highest priorityassignment.

In order to perform priority based arbitration, in one embodiment,guardians 203-1 to 203-H are synchronized with the time base of nodes202-1 to 202-N in order to coordinate the opening and closing oftransmission widows and so that guardians 203-1 to 203-H and nodes 202-1to 202-N agree on the timing of TDMA slots. In one embodiment, thelengths of TDMA slots of different nodes is different and correspond tothe portion of the overall bandwidth assigned to the individual membernode; each TDMA slot allows a specific amount of data transmission. Inone embodiment, for each channel in network 200, the associated guardian203-1 to 203-H is synchronized with network 200 through beaconstransmitted by nodes 202-1 to 202-N, as provided in the '5281application previously referenced and incorporated herein by reference.In one embodiment, network 200 is a TTP network and beacons transmittedby nodes 202-1 to 202-N are action time signals. Further detailsconcerning the synchronization of guardians 203-1 to 203-H with nodes202-1 to 202-N are provided in the '5281 spplication herein incorporatedby reference. In another embodiment, a guardian may open an arbitrationwindow based on the arrival of a first preamble signal, instead of basedon the beginning of a TDMA slot as indicated through beacons transmittedby nodes. In another embodiment, the arbitration window is closed on thereceipt of a second preamble signal and the arbitration winner isdecided immediately.

FIG. 4 is a block diagram of another embodiment of a multi-hub network,shown generally at 400, according to the teachings of the presentinvention. A plurality of hubs 404-1 to 404-X are each coupled to nodes402-1 to 402-T. A plurality of hubs 414-1 to 414-X are each coupled tonodes 412-1 to 412-R. Each hub 404-1 to 404-X is coupled to one hub414-1 to 414-X through an associated communications link 425-1 to 425-Xto create linked hub pairs. The sub-network comprising each linked hubpair and the communications links coupling them to nodes 402-1 to 402-Tand 412-1 to 412-R defines a single communications channel. Each node402-1 to 402-T and 412-1 to 412-R can communicate with every other node402-1 to 402-T and 412-1 to 412-R through the linked hubs. Hubs 404-1 to404-X and 414-1 to 414-X each include a central guardian 403-1 to 403-Xand 413-1 to 403-X that functions to regulate the propagation of datacommunications through each associated channel and across communicationlinks 425-1 to 425-X using priority based arbitration.

Priority based arbitration for network 400 is achieved as follows: Inone embodiment, in operation, each node 402-1 to 402-T and 412-1 to412-R is assigned a priority based on a global priority scheme for eachchannel. For example, in one embodiment nodes 402-1 to 402-T and 412-1to 412-R have an increasing associated global priority of 1 through T+Ron Channel 0. On Channel 1, the priority is reversed so that nodes 402-1to 402-T and 412-1 to 412-R have a decreasing associated priority of T+Rthrough 1. Ideally, each node 402-1 to 402-T and 412-1 to 412-R has fullaccurate knowledge of whether it is permitted to transmit during thecurrent TDMA slot and only one of nodes 402-1 to 402-T and 412-1 to412-R will attempt to transmit data over the channel during any singleTDMA slot. Under these conditions, the guardians 403-1 to 403-X and413-1 to 413-X play a passive role because no arbitration over channeltransmission rights is required. However, under a single failurescenario, a degraded node of 402-1 to 402-T and 412-1 to 412-R mayattempt unauthorized transmissions during a TDMA slot assigned toanother node of 402-1 to 402-T and 412-1 to 412-R. As described withrespect to FIG. 2, priority based arbitration allows only the node withthe highest priority to transmit over the channel. One consequence ofthe global priority scheme of the embodiment described above is that anynode 402-1 to 402-T sending a preamble signal to hub 404-1 (indicatingan intent to transmit over Channel 0) will have priority over any node412-1 to 412-R indicating an intent to transmit to hub 414-1.Accordingly, any node 412-1 to 412-R sending a preamble signal to hub414-2 (indicating an intent to transmit over Channel 1) will havepriority over any node 402-1 to 402-T indicating an intent to transmitto hub 404-2.

On Channel 0 when guardian 403-1 either 1) receives a preamble signalfrom a single node 402-1 to 402-T, or 2) arbitrates a wining node (i.e.a node with the highest priority) after two nodes of 402-1 to 402-T senda preamble signal, then hub 404-1 allows that node to transmit data tohub 414-1 over communications link 425-1. Consequently, guardian 413-1blocks any of nodes 412-1 to 412-R from transmitting over Channel 0because all of hub 414-1's nodes are lower in priority than any of hub404-1's nodes. In contrast, when guardian 413-1 either 1) receives apreamble signal from a single node 412-1 to 412-R, or 2) arbitrates awining node after two nodes of 412-1 to 412-R send a preamble signal,then hub 414-1 allows that node to transmit data to hub 404-1 overcommunications link 425-1 only if guardian 403-1 has not received apreamble from any of nodes 402-1 to 402-T. If guardian 403-1 has notreceived a preamble signal from a higher priority node, then guardian403-1 blocks any of nodes 402-1 to 402-R from transmitting over Channel0 during the time slot.

Because the global priority scheme for Channel 1 is opposite indirection from Channel 0, on Channel 1 when guardian 413-2 either 1)receives a preamble signal from a single node 412-1 to 412-R, or 2)arbitrates a wining node (i.e. a node with the highest priority) aftertwo nodes of 412-1 to 412-R send a preamble signal, then hub 414-2allows that node to transmit data to hub 404-2 over communications link425-2. Consequently, guardian 403-2 blocks any of nodes 402-2 to 402-Tfrom transmitting over Channel 1 because all of hub 404-2's nodes arelower in priority than any of hub 414-2's nodes. In contrast, whenguardian 403-2 either 1) receives a preamble signal from a single node402-1 to 402-T, or 2) arbitrates a wining node after two nodes of 402-1to 402-T send a preamble signal, then hub 404-2 allows that node totransmit data to hub 414-2 over communications link 425-2 only ifguardian 403-1 has not received a preamble from any of nodes 402-1 to402-T. If guardian 413-2 has not received a preamble signal from ahigher priority node, then guardian 413-2 blocks any of nodes 412-1 to412-T from transmitting over Channel 1 during the time slot.

As previously discussed, under a single fault assumption with a network400 of at least two channels having different priority directions,embodiments of the present invention guarantee that a node authorized totransmit by the underlying protocol will have a transmission get throughon at least one channel.

FIGS. 5 a and 5 b are illustrations of embodiments of priority basedarbitration timing diagrams for Channel 0 of a network such as network400 described with respect to FIG. 4 including the global priorityscheme described for Channel 0 with respect to FIG. 4.

In one embodiment, communication links 425-1 to 425-N are full duplexcommunication links allowing communications in both directions betweencoupled hub pairs with priority based arbitration timing 500 asillustrated in FIG. 5 a. Arbitration window 530 opens up for guardian403-1 on the detection of the start of a TDMA slot (shown at 550). Inone embodiment, arbitration time window 530 has a duration of π. Thebounded time interval π represents the maximum skew in the timingsynchronization of nodes 402-1 to 402-T that properly operating nodes402-1 to 402-T are expected to have. In some embodiments, arbitrationwindow 530 has a duration time of π plus a signal propagation delayconstant. Guardian 403-1 arbitrates amongst any of nodes 402-1 to 402-Tthat send a preamble signal (such as preamble signals 525 and 526)during arbitration time window 530. If guardian 403-1 arbitrates awinning node, it allows that node to transmit data to transmit to hub414-1 after arbitration time window 530 closes (shown at 532). Guardian413-1 then blocks nodes 412-1 to 412-R from transmitting during TDMAslot 555 while guardian 403-1 opens a transmission window 540 for thewinning node.

Arbitration window 535 opens up for guardian 413-1 on the detection ofthe start of a TDMA slot (shown at 550). Guardian 413-1 arbitratesamongst any nodes 412-1 to 412-R that send a preamble signal (such aspreamble signals 527 and 528) during arbitration time window 535 inaddition to any winning node resulting from the arbitration of nodes402-1 to 402-T. If guardian 413-1 arbitrates a winning node from nodes412-1 to 412-R, and does not receive any data transmission from guardian403-1 during arbitration time window 535, then guardian 413-1 allows thewinning node to transmit data to hub 404-1 after arbitration time window535 closes (shown at 537). Guardian 403-1 then blocks nodes 402-1 to402-T from transmitting during the TDMA slot while guardian 413-1 openstransmission window 545 for the winning node. Arbitration window 535must be longer in duration than arbitration window 530 because guardian403-1 cannot make an arbitration decision until arbitration window 530closes, and guardian 413-1 must allow guardian 403-1 sufficient time tomake and communicate an arbitration decision before it makes its ownarbitration decision. In one embodiment, arbitration window 535 has aduration of 2π.

If guardian 403-1 does arbitrate a winning node, then guardian 403-1will open transmission window 540 to allow the node to transmit to theother nodes of the channel via hub 404-1, 414-1 and communications link425-1. Meanwhile, guardian 413-1 blocks nodes 412-1 to 412-R fromtransmitting on the channel. If guardian 403-1 does not arbitrate awinning node, then after arbitration window 530 closes, guardian 413-1knows it is safe to open transmission window 545 for one node 412-1 to412-R with the highest priority and allow that node to transmit viacommunication link 225-1 to nodes 402-1 to 402-T.

To make these arbitration decisions, guardians 403-1 and 413-1 do notrequire knowledge of which node should be allowed to transmit per theunderlying protocol. In one embodiment, priority based arbitrationtiming for Channel 1 of network 400 operates the same as described inFIG. 5 except that the global priority is reversed so that nodes 402-1to 402-T and 412-1 to 412-R have a decreasing associated priority of T+Rthrough 1. In that case guardian 403-2 must listen for preamble signalsfrom nodes 402-1 to 402-T and from hub 414-2, so that guardian 403-2must maintain its own arbitration window open for a longer duration toallow for the propagation of an arbitration decision from guardian413-2. Embodiments of the present invention guarantee that a nodetransmission will get through on at least one channel of network 400, aslong each channel has guardian pairs utilizing a different globalpriority direction than the other channels.

In one embodiment, communication links 425-1 to 425-N are half-duplexcommunication links (allowing communications in only one direction at atime between coupled hub pairs) with priority based arbitration timing510 as illustrated in FIG. 5 b. In one embodiment, link 425-1 ishalf-duplex with a default configuration that allows communications onlyfrom 404-1 (the high priority hub) to 404-1 (the low priority hub).Because communication link 425-1 is half-duplex, guardian 403-1 mustarbitrate blindly with respect to guardian 413-1. Arbitration window 560opens up for guardian 403-1 on the detection of the start of a TDMA slot(shown at 590). Guardian 403-1 arbitrates amongst any nodes 402-1 to402-T that send a preamble signal (such as preamble signals 575 and 576)during arbitration time window 560 of duration π. If guardian 403-1arbitrates a winning node, it allows the winning node to transmit to hub414-1 after arbitration time window 560 closes (shown at 562). In themeantime, arbitration window 565 opens up for guardian 413-1 on thedetection of the start of the TDMA slot (shown at 590). Guardian 413-1arbitrates amongst any nodes 412-1 to 412-R that send a preamble signal(such as preamble signals 577 and 578) during arbitration time window565 in addition to notifications from hub 404-1 of any winning noderesulting from the arbitration of nodes 402-1 to 402-T. Arbitrationwindow 565 must be longer in duration than arbitration window 560because guardian 403-1 cannot make an arbitration decision untilarbitration window 560 closes, and guardian 414-1 must allow guardian403-1 sufficient time to make and communicate an arbitration decisionbefore it makes its own arbitration decision. In one embodiment,arbitration window 565 has a duration of 2π. If guardian 403-1 doesarbitrate a winning node, then guardian 403-1 will open transmissionwindow 580 to allow the node to transmit to the other nodes of thechannel via hub 404-1, 414-1 and communications link 425-1 during TDMAslot 595. Meanwhile, guardian 413-1 blocks nodes 412-1 to 412-R fromtransmitting on the channel. If guardian 403-1 does not arbitrate awinning node, then after arbitration window 565 closes guardian 403-1declares hub 414-1 to be the default winner. Then guardian 413-1 knowsit is safe to open transmission window 585 for node 412-1 to 412 R withthe highest priority and allow that node to transmit via communicationlink 225-1 to nodes 402-1 to 402-T during TDMA slot 595.

FIG. 6 is a block diagram of an alternate embodiment of a network, showngenerally at 600, according to the teachings of the present invention.Node 600 includes hub and bus configurations. Hubs 604-1 to 604-N areeach coupled directly to nodes 602-1 to 602-P. Nodes 612-1 to 612-D areeach coupled to buses 625-1 and 625-2. Buses 625-1 and 625-2 are coupledto each of hubs 604-1 and 604-2. In operation each nodes 602-1 to 602-Pand 612-1 to 612-D sends one frame on each of the N channels duringevery TDMA round. In one embodiment, the priority arbitration schemesprovided throughout this application are applicable to arbitratingbetween the nodes 602-1 and 602-P (i.e. nodes coupled directly with hubs604-1 to 604-N) and N channel busses 625-1 and 625-2 where each bus istreated as a single node for priority arbitration purposes.

FIG. 7 is a flow chart of one of a method of priority based arbitrationfor a central guardian of one channel of a TDMA multi-channel network,shown generally at 700. The method initially comprises assigning aunique priority rank to each node coupled to the channel (710) whereinthe unique priority rank direction for the nodes of the one channel isdifferent than the unique priority rank direction of another channel ofthe multi-channel network. The method proceeds with observing thereceipt of a first preamble signal (720) indicating the intention of afirst node to transmit during the time slot and observing the receipt ofa second preamble signal (730) indicating the intention of a second nodeto transmit during the time slot within a predefined time interval ofobserving the receipt of the first preamble signal. When the first nodehas a higher priority rank than the second node, the method continueswith allowing only the first node to transmit through the one channelduring the time slot (740). When the second node has a higher priorityrank than the first node, the method continues with allowing only thesecond node to transmit through the one channel during the time slot(750).

By removing the requirement to store schedule information in the Hub thefollowing advantages are achieved:

-   -   a. Removal of the tool issues relating to Central Guardian        Schedule Table development and verification of Central Guardian        Schedule correctness.    -   b. Reduction in complexity of a central guardian relieving it        from the need to store and utilize Central Guardian Schedule        Table information.    -   c. Reduction in hub-state space and susceptibility to single        event upset (SEU). In one embodiment, single event upset is        based on upsets induced by high energy neutrons. Embodiments of        the present invention reduce SEU by having no required schedule        position related state for a guardian to keep track of.        Therefore, there is no state to be upset.    -   d. Removal of Guardian's semantic dependency on protocol state        signals        -   Enabling of the Central Guardian to enforce across TDMA            Protocol Mode changes that result in different transmission            order, without the hub processing mode change signals.        -   Enabling of Multiplexed Nodes to shared TDMA Slots, without            the hub following schedule position.            In one embodiment, simple heuristics is added to further            enhance the resilience of the guardian in the above            described systems. In one embodiment, if a node is showing            activity prior to its time slot, it could be disabled from            taking part in the arbitration. This effectively contains a            node sending errant preamble signals or any node that is not            synchronized to the network. In another embodiment once a            node has won arbitration it may be blocked and prevented            from arbitrating for 1 or more slots.

In one embodiment a centralized guardian of the present invention isfurther adapted to modify messages transmitted through the associatedhub with an identifier derived from the port number the originating nodeis coupled to, as detailed in the '7587 application herein incorporatedby reference. Accordingly, a node simultaneously receiving two differentmessages on diverse channels can identify the two nodes transmitting themessages and, in one embodiment, choose to accept only the message fromthe node authorized by protocol to transmit during the TDMA slot.Further details pertaining to port driven authentication in a network asdescribed above can be found in the '7587 application.

Several ways are available to implement the central guardian element ofthe current invention. These include, but are not limited to, digitalcomputer systems, programmable controllers, or field programmable gatearrays. Therefore other embodiments of the present invention are theprogram instructions resident on computer readable media which whenimplemented by such controllers, enable the controllers to implementembodiments of the present invention. Computer readable media includeany form of computer memory, including but not limited to magnetic diskor tape, CD-ROMs, DVD-ROMs, or any optical data storage system, flashROM, non-volatile ROM, or RAM.

A number of embodiments of the present invention have been described.Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiment shown. It will beunderstood that various modifications to the described embodiments maybe made without departing from the scope of the claimed invention. Thisapplication is intended to cover any adaptations or variations of thepresent invention. Therefore, it is manifestly intended that thisinvention be limited only by the claims and the equivalents thereof.

1. A multi-channel network having priority based arbitration, thenetwork comprising: a plurality of nodes, wherein each of the pluralityof nodes is adapted to transmit and receive data; two or more hubs, eachhub having communication links with the plurality of nodes, wherein thecommunication links between any one hub and the plurality of nodesdefines a first channel of the multi-channel network; wherein each nodeis adapted to communicate with every other node through the two or morehubs; and two or more guardians, wherein each guardian is associatedwith one of the two or more hubs; wherein each node is adapted totransmit during a time slot; wherein for each channel of themulti-channel network, each node is assigned a unique priority rank;wherein for each channel of the multi-channel network, the uniquepriority rank for each of the plurality of nodes are in differentdirections; wherein a first of the two or more guardians determineswhich of the plurality of nodes is permitted to transmit data duringassociated time slots by permitting only a winning node with the highestassigned priority rank to transmit through the channel.
 2. The networkof claim 1, further comprising: one or more electronic devices incommunication with the plurality of nodes, wherein the one or moreelectronic devices include one or more of: sensors, processors,actuators, controllers, and input devices.
 3. The network of claim 1,wherein the multi-channel network is a TDMA network and the time slot isa TDMA slot.
 4. The network of claim 1, wherein the multi-channelnetwork is a TTP/C protocol network.
 5. The network of claim 1, whereineach of the two or more guardians is located within an associated hub ofthe two or more hubs.
 6. The network of claim 1, wherein each node ofthe plurality of nodes transmits an preamble signal to the two or moreguardians to indicate the intention to transmit.
 7. The network of claim6, wherein preamble signals are transmitted from each node of theplurality of nodes to the two or more guardians on communication linkscarrying data.
 8. The network of claim 6, wherein preamble signals aretransmitted from each node of the plurality of nodes to the two or moreguardians on communication links other than communication links carryingdata.
 9. The network of claim 6, wherein the first guardian is adaptedto observe the receipt of a first preamble signal from a first node ofthe plurality of nodes; wherein when the first guardian observes thereceipt of a second preamble signal from a second node of the pluralityof nodes within a predefined time interval, then the first guardianpermits only one of the first node or the second node to transmitthrough the associated channel; wherein the first guardian permits thefirst node to transmit if the first node has a higher priority rank thanthe second node; wherein the first guardian permits the second node totransmit if the second node has a higher priority rank than the firstnode; wherein when the first guardian does not observe the receipt of asecond preamble signal within the predefined time interval, the firstguardian permits the first node transmit through the associated channel.10. The network of claim 9, wherein the predefined time interval isequal to π.
 11. The network of claim 9, wherein the predefined timeinterval is equal to π plus a signal propagation delay constant.
 12. Thenetwork of claim 1, wherein each guardian further comprises: a memory,wherein the unique priority ranking for each node of the plurality ofnodes is stored in the memory.
 13. The network of claim 12, wherein thememory can be reprogrammed to change unique priority ranking for eachnode of the plurality of nodes.
 14. The network of claim 13, wherein thememory can be reprogrammed through the plurality of nodes.
 15. Thenetwork of claim 1, wherein each hub further comprises: a plurality ofports, wherein each node of the plurality of nodes is coupled to eachhub of the two or more hubs through one port; wherein, the uniquepriority ranking for each node of the plurality of nodes is determinedby which port of the plurality of ports, it is coupled to.
 16. Thenetwork of claim 1, wherein each guardian of the two or more guardiansis synchronized with the plurality of nodes though a plurality ofbeacons transmitted by a plurality of the plurality of nodes.
 17. Thenetwork of claim 1, wherein nodes of the plurality of nodes and the twoor more guardians are adapted to implement port driven authentication;wherein when nodes of the plurality of nodes receive differing data ondiverse channels, the nodes of the plurality of nodes accept data onlyfrom an authorized node; wherein the authorized node is the node of theplurality of nodes authorized by protocol to transmit during the timeslot.
 18. A network, comprising: a plurality of sub-networks; and aplurality of nodes adapted to transmit and receive data, wherein througheach sub-network every node is coupled to communicate with every othernode; wherein for each sub-network each node is assigned a uniquepriority rank; wherein one winning node of the plurality of nodes isidentified as having the highest priority rank for at least onesub-network and is permitted to transmit during a time slot; wherein foreach sub-network the plurality of nodes are ranked in a differentpriority direction.
 19. The network of claim 18, further comprising: oneor more electronic devices in communication with the plurality of nodes,wherein the one or more electronic devices include one or more of:sensors, processors, actuators, controllers, and input devices.
 20. Thenetwork of claim 18, wherein the network is a TDMA network.
 21. Thenetwork of claim 18, wherein the network is a TTP/C protocol network.22. The network of claim 18, wherein a first sub-network of theplurality of sub-networks further comprises: one or more hubs, whereineach node of the plurality of nodes is coupled to at least one hub ofthe one or more hubs, wherein the one or more hubs are adapted tocommunicate with each other.
 23. The network of claim 22, wherein theone or more hubs communicate to each other over one or more full duplexcommunication links.
 24. The network of claim 22, wherein the one ormore hubs communicate to each other over one or more half duplexcommunication links.
 25. The network of claim 22, each sub-network ofthe plurality of sub-networks further comprising: one or more guardians,wherein each guardian of the one or more guardians is associated withone hub of the one or more hubs, wherein the one or more guardians allowonly the one winning node of the plurality of nodes with the highestpriority rank to transmit through the sub-network during the time slot.26. The network of claim 25, wherein each node of the plurality of nodestransmits a preamble signal when it intends to transmit.
 27. The networkof claim 26, wherein preamble signals and data are diverselycommunicated from each node of the plurality of nodes to the one or moreguardians.
 28. The network of claim 26, wherein each guardian of the oneor more guardians is adapted to observe the receipt of a first preamblesignal from a first node; wherein when a first guardian of the one ormore guardians observes the receipt of a second preamble signal from asecond node within a predefined time interval, then the first guardianpermits only one of the first node or the second node to transmitthrough the associated sub-network; wherein the first guardian permitsthe first node to transmit if the first node has a higher priority rankthan the second node; wherein the first guardian permits the second nodeto transmit if the second node has a higher priority rank than the firstnode; wherein when the first guardian does not observe the receipt of asecond preamble signal within the predefined time interval, the firstguardian permits the first node transmit through the associated channel.29. The network of claim 28, wherein each guardian of the one or moreguardians has a different predefined time interval based on the relativepriority of nodes coupled directly to the guardian's associated hub. 30.The network of claim 25, wherein each guardian of the one or moreguardians further comprises: a memory, wherein unique priority ranks fornodes is stored in the memory.
 31. The network of claim 30, wherein thememory can be reprogrammed to change unique priority ranking for eachnode of the plurality of nodes.
 32. The network of claim 31, wherein thememory can be reprogrammed through the plurality of nodes.
 33. Thenetwork of claim 25, wherein each hub of the one or more hubs furthercomprises: a plurality of ports, wherein each node of the plurality ofnodes is coupled to each hub of the one or more hubs through one port ofthe plurality of ports, wherein, the unique priority rank for each nodeof the plurality of nodes is determined by which port of the pluralityof ports, the node is couple to.
 34. The network of claim 25, whereineach guardian of the one or more guardians is synchronized with theplurality of nodes though a plurality of beacons transmitted by theplurality of nodes.
 35. The network of claim 25, wherein nodes of theplurality of nodes and the one or more guardians are adapted toimplement port driven authentication; wherein when nodes of theplurality of nodes receive differing data on diverse channels, the nodesof the plurality of nodes accept data only from an authorized node;wherein the authorized node is the node of the plurality of nodesauthorized by protocol to transmit during the time slot.
 36. A method ofpriority based arbitration for a central guardian of one channel of aTDMA multi-channel network, the method comprising: assigning a uniquepriority rank to each of a plurality of nodes coupled to the onechannel; observing the receipt of a first preamble signal indicating theintention of a first node of the plurality of nodes to transmit during atime slot; observing the receipt of a second preamble signal indicatingthe intention of a second node of the plurality of nodes to transmitduring the time slot within a predefined time interval of observing thereceipt of the first preamble signal; when the first node has a higherpriority rank than the second node, allowing only the first node totransmit through the one channel during the time slot; and when thesecond node has a higher priority rank than the first node, allowingonly the second node to transmit through the one channel during the timeslot; wherein for each channel of the multi-channel network, the uniquepriority rank direction is different.
 37. A network comprising: meansfor priority based arbitration for a centralized guardian with aplurality of nodes of a multi-channel network; means for assigning aunique priority rank to each of the plurality of nodes coupled to afirst channel of the multi-channel network; means for observing thereceipt of a first preamble signal indicating the intention of a firstnode of the plurality of nodes to transmit during the a time slot; meansfor observing the receipt of a second preamble signal indicating theintention of a second node of the plurality of nodes to transmit duringthe time slot within a predefined time interval of observing the receiptof the first preamble signal; when the first node has a higher priorityrank than the second node, means for allowing only the first node totransmit during the time slot; and when the second node has a higherpriority rank than the first node, means for allowing only the secondnode to transmit during the time slot; wherein for each channel of themulti-channel network, the unique priority rank direction is different.38. A computer-readable medium having computer-executable instructionsfor performing a method of priority based arbitration for a centralguardian of one channel of a TDMA multi-channel network, the methodcomprising: assigning a unique priority rank to each node of a pluralityof nodes coupled to the one channel; observing the receipt of a firstpreamble signal indicating the intention of a first node of theplurality of nodes to transmit during the a time slot; observing thereceipt of a second preamble signal indicating the intention of a secondnode of the plurality of nodes to transmit during the a time slot withina predefined time interval of observing the receipt of the firstpreamble signal; when the first node has a higher priority rank than thesecond node, allowing only the first node to transmit through the onechannel during the time slot; and when the second node has a higherpriority rank than the first node, allowing only the second node totransmit through the one channel during the time slot; wherein for eachchannel of the multi-channel network, the unique priority rank directionis different.